your options are literially call the stores and hope, failing that, pay 6 quid more and deal, or TRY the tesco brand and see if it's comparable, you're out what? 12 pounds if it's shit? if you're traveling and not budgeting for "oops" then you need to learn to travel better!
Or simply visit the chemist's and walk away with the item. Why even go through the hassle of ordering something online, waiting till the next day and paying 6 quid more? It's stupid. You could walk out of the chemist's shop with the item you wanted immediately instead of settling with rubbish or waiting a day and paying more.